The present invention relates to a system and method for injecting fuel into a chamber of an air intake manifold having a plurality of branch passages to intake ports of cylinders of an internal combustion engine.
In a premixture type gasoline engine, at least one fuel injector is disposed so as to inject fuel into a chamber of an air intake manifold of the engine in order to achieve a predetermined air-fuel mixture ratio and supply rate for the air fuel mixture to be supplied to the engine according to engine load. The chamber is connected to a plurality of engine cylinders via a plurality of branch passages.
Such conventional fuel injection systems as described above are exemplified by a Japanese Publication "Toyota Technology" published on June, 1984 in pages 55 to 61.
In the above-identified Japanese document, two fuel injectors are disposed within a chamber defining a junction of a plurality of branch passages connected to the respective engine cylinders to inject fuel for first through sixth engine cylinders. It is noted that two fuel injectors are disposed upstream of a throttle valve and a heater is disposed downstream of the throttle valve to promote atomization of fuel injected through the fuel injectors. An intermediate position of the intake manifold downstream of the heater forms branches into a plurality of passages, each communicating with an intake port of a corresponding cylinder.
The fuel injectors inject fuel supplied from a fuel supply apparatus in synchronization with a suction stroke of each cylinder so as to provide the predetermined air-fuel mixture ratio. In the case disclosed in the above-identified Japanese Publication, the amount of fuel to be injected by the injectors is calculated by means of a control unit according to engine load (as determined by intake air quantity). The calculation operation is repeated in synchronization with engine revolution. The same amount of fuel, which is derived in one calculation operation, is injected by the injectors to each of the engine cylinders in the corresponding engine cycle. The injected fuel, at this time, flows from the junction through each of the branch passages to the respective cylinders in sequence. The timing of the injection pulses is calculated and controlled to correspond to the suction strokes of the respective cylinders.
In the conventional fuel injection system disclosed in the above-identified Japanese document, a time it takes for the injected fuel from the injectors to arrive at the respective cylinders is different because the branch passages are not of equal length and the air stream in the intake manifold has an influence on the arrival times of the injected fuel to the respective cylinders. Therefore, when a uniform amount of fuel is injected via the fuel injectors in the suction stroke of each cylinder, the respective amounts of fuel actually sucked into the respective cylinders are unequal.
Since distribution of fuel into the respective cylinders is also affected by the engine revolution speed and engine load (e.g., intake air quantity), consequently a rich air-fuel mixture ratio for some cylinders and a thin air-fuel mixture ratio for other cylinders are found. Therefore, fuel economy becomes reduced, torque output of the engine becomes varied due to unstable combustion, and engine vibration due to unequal torque output between the individual cylinders is increased. Furthermore unstable combustion characteristics cause emission control problems.